Selective catalytic reduction (“SCR”) exhaust aftertreatment systems are an important technology for reducing NOx emissions from internal combustion engines such as diesel engines. SCR systems generally include a source of storage for the diesel exhaust fluid (DEF), a doser that includes at least one of a pump unit for pressurizing the DEF and a metering unit for providing a controlled amount or rate of DEF, and an injector which provides urea solution to a DEF decomposition region of an exhaust flow path located upstream from an SCR catalyst. Many SCR systems also utilize pressurized gas to assist the flow of DEF to the injector. While providing important reductions in NOx emissions, SCR systems suffer from a number of shortcomings and problems.
For example, the nozzle for injecting DEF into the exhaust system is typically mounted to or within the exhaust system. At high exhaust temperatures, the nozzle is also heated. The heated nozzle can vaporize the water in the DEF at the start of the injection cycle until the nozzle is sufficiently cooled by the DEF flow. This vaporization results in a large pressure wave that expands upstream from the nozzle through the doser system, increasing the potential for damage and repairs. Thus, there is a need for advancements mitigating these and other shortcomings associated with injection systems for delivery of DEF through a nozzle connected to an exhaust system.